Heat exchangers that are known from the prior art, in particular heat exchangers embodied as condensers in refrigeration circuits and air conditioning systems that use R134a as the refrigerant, are designed, based on the operating pressures and requirements of the systems, for burst pressures of 60 bar.
These heat exchangers have flow channels for the refrigerant that are designed as flat tubes through which the refrigerant flows in one or more rows in a single-flow or multi-flow configuration. The ends of each of the flat tubes lead to a header tube provided for more than one flat tube combined. The header tube thus serves to collect the refrigerant flowing through the individual flat tubes or to distribute the refrigerant to the individual flat tubes. Inside the header tube, the mass flow of refrigerant is redirected. Traditionally, particularly in air-refrigerant heat exchangers, fins are arranged between adjacent flat tubes.
The header tubes of the heat exchangers are embodied as integral or as having two parts. The flat tubes are arranged extending through openings in the wall, through the wall and into the interior of the header tube. Thus the inner volume of the header tube is connected to the inner volumes of the flat tubes.
A header tube for a heat exchanger, in particular for a condenser of a refrigeration circuit, is disclosed in DE 93 21 403 U1. A header tube, provided as a manifold or connecting tube, is embodied as having a plurality of slot-shaped openings arranged in its lateral surface. The openings extend with a longitudinal axis transversely to a longitudinal axis of the header tube. Some of the plurality of openings are intended to receive heat exchange tubes, while the remaining openings are designed to receive partitions.
To produce such header tubes, punches that penetrate radially into the header tube are provided, which produce the openings as they penetrate the tube. The heat exchange tubes, which are embodied particularly as flat tubes, are then inserted with one end into the openings and soldered to the header tube forming a seal.
With known prior art header tubes for heat exchangers, the slot-type openings for the flat tubes are punched or milled into the free cross-section of the tube.
FIGS. 1a and 1b each show a prior art device 1′ for a heat exchanger for collecting and distributing a heat exchange fluid, having a header tube 2 embodied as integral and a plurality of flat tubes 6. FIG. 1a shows a sectional illustration from a plan view in the direction of the longitudinal axis of the header tube 2. FIG. 1b shows a perspective view.
The flat tubes 6 have inner flow channels 7 arranged parallel to one another and aligned along a longitudinal axis of the flat tubes 6, which channels are charged with fluid simultaneously when the heat exchanger is in operation.
The header tube 2, which serves as distributor or collector for the heat exchange fluid, is embodied as having through openings 5 arranged in a wall 3, also referred to as the lateral surface of the hollow cylindrical header tube 2. Through openings 5 are aligned with a longitudinal extension perpendicular to the longitudinal axis of header tube 2, and are designed to receive the flat tubes 6. A cross-sectional shape of through openings 5 is substantially the same as an outer circumferential shape of flat tubes 6, and the through openings 5 are designed as having only a tolerance with respect to the circumferential shape of the flat tubes 6 that is necessary for assembly. Circumferential shape in this case is understood as a profile perpendicular to the longitudinal axis of the flat tubes 6.
When the device 1′ is in an assembled and soldered state, ends of the flat tubes 6 are arranged in the through the openings 5 in such a way that inner volumes of the flow channels 7 and an inner volume of the header tube 2 are interconnected. The inner volume of the header tube 2 is delimited by the wall 3, which also defines an inner cross-section 4 of the header tube 2, also referred to as the free cross-section 4. The ends of the flat tubes 6 project into the free cross-section 4.
The flat tubes 6, which are embodied as having a narrow side and a wide side, have a width b′ across the wide side. The flow channels 7 are arranged side by side in the direction of the wide side.
The header tube 2 is embodied as a hollow cylinder according to FIGS. 1a and 1b, and has a circular free cross-section 4, enclosed by the circular wall 3 having a wall thickness s′. The free cross-section 4 is defined by an inner diameter d′. An outer diameter D′ of the header tube 2 is the sum of the inner diameter d′ plus twice the wall thickness s′.
When the device 1′ is in the assembled state, the flat tubes 6 are aligned perpendicular to the longitudinal axis of the header tube 2 with their wide sides parallel to one another. The flat tubes 6, which have the width b′, are therefore also parallel to the annular inner cross-section 4 of the header tube 2, which has the inner diameter d′. The inner diameter d′ is known to be the greatest possible distance between two points on the circumferential line of the inner cross-section 4 and therefore the greatest dimension perpendicular to the longitudinal axis of the header tube 2.
Since the widths b′ of the flat tubes 6 are smaller than the inner diameter d′ of the free cross-section 4 of the header tube 2 and since the flat tubes 6 are aligned centered in relation to the longitudinal axis of the header tube 2, the through openings 5 extend only in the region of the free cross-section 4. The wall 3 of the header tube 2 is penetrated during the production of the through openings 5 in such a way that the slot-type through openings 5 for the flat tubes 6 extend from the outer side of the wall 3 up to the free cross-section 4 of the header tube 2.
The flat tubes 6, which are inserted into the through openings 5 through the wall 3 when device 1′ is in the assembled state, end within the free cross-section 4, with the ends of the flat tubes 6 spaced from the wall 3 and not in contact with the wall 3 when they are sufficiently inserted.
When conventional devices l′ from FIGS. 1a and 1b are used with the known combination of the header tube 2 having a wall thickness s′ of 1 mm, for example, and the connection thereof to the flat tubes 6 having a width b′ ranging from 10.0 mm to 16.0 mm, for example, for applications involving carbon dioxide as refrigerant, and thus with substantially higher pressures, an adjustment of the configuration to the necessary burst pressure of 340 bar at 160° C. would result in substantially greater wall thicknesses s′ and outer diameters D′. With a width b′ of the flat tube 6 of 12.0 mm and a resulting wall thickness s′ ranging from 3.0 mm to 4.0 mm, the header tube 2 would have an outer diameter D′ ranging from 20.0 mm to 22.0 mm. The costs and the weight of the heat exchanger would increase significantly. The amount of space required for the heat exchanger would also increase substantially.
The flat tube 6 is also embodied as having a solder dam 11′ in the form of a notch or groove. The solder dam 11′ is formed on the surface of the flat tube outside of the wall 3 of the header tube 2, and is aligned perpendicular to the longitudinal axis of the flat tube 6. During the soldering process, the solder dam 11′ prevents liquid solder from flowing away from the wall 3 along the surface of the flat tube 6, or in the case of air-refrigerant heat exchangers, for example, in the direction of air plates or fins formed on the surface.